mumbling n grumbling at a stop light

hello all, ben awhile. enjoyin my new 360, ben puttin quite a few miles on er. 360 bored over kb slugs 9.5 somethin ratio comp cam 480 lift? dual plain intake, eddy carb just rebuilt, long tube headers, stock distributor, msd wires. msd coil. 2200 stall convertor

but, doesnt like sitting at a stop light. after a half hour or so of drivin around (to get hot) she mumbles at a stop light, almost like its forgeting to fire a cylinder. the more stop lights i sit at the worse it gets, occasionaly it will just shut off. 750 rpm, 1000 when not in gear. if i lightly step on the go button, stops grumblin. whats goin on? messed around with timing and seems not help wherever i put it (at about 34 right now) runs like a champ otherwise.

carb need adjusting? or time to get a new distributor? (recently rebuilt) timing being goofy? (all in specs)

dad said to try premium gas, ill see what that does later. most likely something really simple, but i like hearing what you guys have to say